Really the fracturedness and poor leadership China had at the time was only thing Japan really had going for it. The Japanese army wasn’t all that much better equipment then the Chinese were. Whenever the Japanese went up against the Soviets, they got absolutely stomped.

I’d argue that what really defeated the Japanese was pro-Japanese Chinese officials getting removed in various protests in the years prior to the 2nd Sino-Japanese war. Japan was very much trying to do the same strategy of incremental subjugation towards Asia that the US today does to Europe via NATO.

All I know are that the Communists and Chinese Nationalists make a cease fire to defend from the Japanese invasion, that the Americans did provide military support, and that the European colonizers work with the colonized people for the defense. The Japanese Fascists now have good opinions toward Americans, but they were brutal towards the Americans at that time which help in the unified resistance.